We are studying the development of the resting potential, action potential and generator potential in embryonic primary sensory neurons. Rohon-Beard cells are found in the dorsal portion of the spinal cord of amphibian tadpoles (Xenopus laevis). These cells have a resting potential equal to the potassium equilibrium potential. They behave like potassium electrodes and are depolarized by the accumulation of K ion in the extracellular space resulting from impulse activity of other neurons. These cells initially have action potentials of long duration dependent on Ca ions; later Na ion and Ca ions carry inward current, finally Na ion alone. We are presently recording from these cells while poking the skin on the flank of the tadpowl with a stylus, to investigate the generator potential and study receptive field development. Bibliographic references: Time of origin of Rohon-Beard neurons in spinal cord of Xenopus Laevis. Janet L. Spitzer and Nicholas C. Spitzer. American Society of Zoologists, Meeting August 1975; Changes in the ionic basis of the action potential in Rohon-Beard neurons during development. Nicholas C. Spitzer & Paola I. Baccaglini. Society for Neuroscience, Meeting November 1975.